1. Field of the Invention
The present invention relates to an ophthalmologic apparatus capable of measuring distance in the oculus of an eye.
2. Description of the Related Art
For an ophthalmologic apparatus for measuring distance in the oculus of an eye (e.g., axial length), a method of utilizing ultrasonic waves and a method of utilizing light are commonly employed. A method of utilizing ultrasonic waves is disclosed, for example, in JP Patent laid-open No. 2001-61784. In addition, the method of utilizing light is disclosed in JP Patent laid-open No. Hei 5-277075.
Methods of utilizing ultrasonic waves are problematic in that they impose mental and physical strain on the subject during measurement by bringing an ultrasonic probe into contact with the cornea of the eye (more specifically, by indirect contact via liquid or gel ultrasonic waves medium). Moreover, since the eye needs to be disinfected prior to measurement, it is problematic in that the work takes time or imposes strain on the subject. On the other hand, methods of utilizing light have an advantage in that strain on the subject is smaller than in the case of ultrasonic waves and work such as disinfecting is not required since measurement is possible without contact with the eye.
Herein, as an example of the ophthalmologic apparatus according to the present invention, the related art of an apparatus is described in “Preferred Embodiment of the Invention”. This apparatus is comprised of a fundus camera and an OCT (Optical Coherence Tomography) technology applied apparatus (referred to as optical image measuring device, light coherence tomography apparatus, and so on.).
FIG. 14 shows one example of the appearance of a conventional fundus camera in general, and FIG. 15 shows one example of an optical system composition to be internally accommodated therein (e.g. JP Patent laid-open No. 2004-350849). This fundus camera 1000 is provided with a platform 3 mounted on a base 2 slidably in the front and rear, right and left (horizontal direction) directions. On this platform 3, an operation panel 3a and a control lever 4 are installed for an examiner to conduct various operations.
The examiner may place the platform 3 on the base 2 to be moved 3-dimensionally by operating the control lever 4. On the top of the control lever 4, an operation button 4a is installed to be pressed down to obtain fundus oculi images.
On the base 2, a post 5 is installed standing upwards. On the post 5, a jaw rest 6 where the jaw of a patient is to be rested and an external fixation lamp 7 as a light source for fixing an eye E are provided.
On the platform 3, a main body part 8 is installed to accommodate various optical systems or control systems of the fundus camera 1000. Furthermore, the control system may be installed inside the base 2 or the platform 3, etc., or in an external device such as a computer, etc. connected to the fundus camera 1000.
On the side of the eye E of the main body part 8 (the left side of the page in FIG. 14), an objective lens part 8a disposed opposite the eye E is installed. Also, on the examiner's side of the main body part 8 (the right side of the page in FIG. 14), an objective lens part 8b for observing the fundus oculi of the eye E with the naked is installed.
Furthermore, connected to the main body part 8 is a still camera 9 for producing a still image of a fundus oculi of the eye E and an imaging device 10 such as a TV camera, etc. for producing still images or moving images of a fundus oculi. The still camera 9 and the imaging device 10 are formed removably with respect to the main body part 8.
As a still camera 9, in accordance with various conditions such as the purpose of an examination or the saving method of produced images, etc., a digital camera equipped with imaging elements such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), a film camera, and an instant camera, etc. may interchangeably be used when it is appropriate. The main body part 8 is equipped with a mounting part 8c for interchangeably mounting such a still camera 9.
If the still camera 9 or the imaging device 10 is for taking digital images, the image data of the produced fundus image may be sent to a device such as a computer, etc. connected to the fundus camera 1000 and be observed as a fundus image by being displayed on the display. Also, the image data can be sent to an image storing device connected to the fundus camera 1000 to compile a database and be used as electronic data for creating medical charts, etc.
Furthermore, on the examiner's side of the main body part 8, a touch panel monitor 11 is installed. On this touch panel monitor 11, fundus images of the eye E created based on the video signals output from the still camera 9 (a digital method thereof) or the imaging device 10 are displayed. Moreover, on the touch panel monitor 11, the 2-dimensional coordinate system with the center of the screen as the origin is displayed overlapped with a fundus image. When the screen is touched by the examiner, the coordinate value corresponding to the touched position is displayed.
Next, referring to FIG. 15, a composition of an optical system of the fundus camera 1000 is described. The fundus camera 1000 is provided with an illuminating optical system 100 to light the fundus oculi Ef of an eye E, an imaging optical system 120 to guide the fundus reflection light of the illumination light to the eyepiece part 8b, a still camera 9, and an imaging device 10.
The illuminating optical system 100 comprises: an observation light source 101, a condenser lens 102, an imaging light source 103, a condenser lens 104, an exciter filter 105 and 106, a ring transparent plate 107, a mirror 108, a liquid crystal display (LCD) 109, an illumination diaphragm 110, a relay lens 111, an aperture mirror 112, and an objective lens 113.
The observation light source 101 consists of a halogen lamp, etc. and emits continuous light for observing the fundus. The condenser lens 102 is an optical element that converges the continuous light (observation illumination light) emitted by the observation light source 101 and substantially evenly irradiates the observation illumination light to the fundus oculi.
The imaging light source 103 consists of a xenon lamp, etc. to be flashed when producing fundus oculi Ef images. The condenser lens 104 is an optical element that converges the flash light (imaging illumination light) emitted by the imaging light source 103 and irradiates the fundus oculi Ef evenly with the imaging illumination light.
The exciter filters 105 and 106 are the filters to be used when fluorography of images of a fundus oculi Ef takes a place. The exciter filters 105 and 106 respectively can be inserted and removed on the optical path by a drive mechanism such as a solenoid, etc. The exciter filter 105 is disposed on the optical path in the event of FAG (fluorescein angiography). Whereas, the exciter filter 106 is disposed on the optical path in the event of ICG (indocyanine green angiography). Furthermore, when color images are being obtained, both exciter filters 105 and 106 are retracted from the optical path.
The ring transparent plate 107 is disposed in a conjugating location with a pupil of the eye E, and is equipped with a ring transparent part 107a taking an optical axis of the illuminating optical system 100 as a center. The mirror 108 reflects the illumination light emitted by the observation light source 101 or by the imaging light source 103 in the direction of the optical axis of the imaging optical system 120. The LCD 109 displays a fixation target (not illustrated) for fixing the eye E.
The illumination diaphragm 110 is a diaphragm member to shut out a part of the illumination light for flare prevention, etc. This illumination diaphragm 110 is composed movably in the light axial direction of the illuminating optical system 100, and is thus capable of changing the illuminating region of the fundus oculi Ef.
The aperture mirror 112 is an optical element to combine an optical axis of the illuminating optical system 100 and an optical axis of the imaging optical system 120. In the center region of the aperture mirror 112 an aperture part 112a is opened. The light axis of the illuminating optical system 100 and the light axis of the imaging optical system 120 are to be crossed at a substantially central location of this aperture part 112a. The objective lens 113 is installed in the objective lens part 8a of the main body part 8.
The illuminating optical system 100 having such a composition illuminates a fundus oculi Ef in the following manner. First, the observation illumination light is emitted when the observation light source 101 is lit during fundus observation. This observation illumination light irradiates the ring transparent plate 107 through the condenser lenses 102 and 104. (The exciter filters 105 and 106 are removed from the optical path.) The light passed through the ring transparent part 107a of the ring transparent plate 107 is reflected by the mirror 108 and is reflected along the optical axial direction of the imaging optical system 120 due to the aperture mirror 112 through the LCD 109, the illumination diaphragm 110 and the relay lens 111. The observing illumination light reflected by the aperture mirror 112 advances in the optical axial direction of the imaging optical system 120 and is converged by the objective lens 113, to be made incident onto the eye E, and illuminates the fundus oculi Ef.
Then, the ring transparent plate 107 is disposed in a conjugating location with the pupil of the eye E, and on the pupil a ring shaped image of the entering observation illumination light is formed. The fundus reflection light of the entered observation illumination light is to be emitted from the eye E through a central dark part of the ring image on the pupil. As described, it is to protect the effect of observing illumination light entering the eye E with respect to the fundus reflection light of the observing illumination light.
On the other hand, when imaging the fundus oculi Ef, flush light is emitted from the imaging light source 103 and the imaging illumination light is irradiated onto the fundus oculi Ef through the same path. In the event of photofluographing, either the exciter filter 105 or the exciter filter 106 is disposed selectively on the optical path depending on whether FAG imaging or ICG imaging is carried out.
Imaging optical system 120 comprises: an objective lens 113, an aperture mirror 112 (an aperture part 112a thereof), an imaging diaphragm 121, a barrier filter 122 and 123, a focusing lens 124, a relay lens 125, an imaging lens 126, a quick return mirror 127 and an imaging media 9a. Herein, the imaging media 9a is an arbitrary imaging media (image pick-up elements such as CCD, camera film, instant film, etc.) used for a still camera 9.
The fundus reflection light of the illumination light, emitted through the central dark part of the ring shaped image formed on the pupil from the eye E, enters the imaging diaphragm 121 through the aperture part 112a of the aperture mirror 112. The aperture mirror 112 reflects cornea reflection light of the illumination light and acts so as not to mix the cornea reflection light into the fundus reflection light made incident onto the imaging diaphragm 121. As a result, the generation of flare on the observation images and/or produced images is prevented.
The imaging diaphragm 121 is a plate shaped member at which plural circular light transparent parts of different sizes are formed. The plural light transparent parts constitute different diaphragms with different diaphragm values (F value), and are to be disposed alternatively on the optical path by a drive mechanism (not illustrated herein).
The barrier filters 122 and 123 can be inserted and removed on the optical path by a drive mechanism such as a solenoid, etc. In the event of FAG imaging, the barrier filter 122 is disposed on the optical path while in the event of ICG imaging the barrier filter 123 is inserted onto the optical path. Furthermore, when producing color images the barrier filters 122 and 123 are to be retracted from the optical path.
The focusing lens 124 is to be movable in the light axial direction of the imaging optical system 120 by a drive mechanism (not illustrated herein). This makes it possible to change the magnifying ratio of an observation and the magnifying ratio in imaging, and to focus images of a fundus oculi. The imaging lens 126 is a lens to focus the fundus reflection light from an eye E on the imaging media 9a. 
The quick return mirror 127 is disposed rotatably around a rotary shaft 127a by a drive mechanism not illustrated herein. In the event of imaging a fundus oculi Ef with the still camera 9, the fundus reflection light is supposed to be guided to the imaging media 9a by springing up the quick return mirror 127 that is obliquely mounted on the optical path. Whereas, in the event of imaging a fundus oculi with an imaging device 10 or of observing the fundus oculi with the naked eye of the examiner, the quick return mirror 127 is to be obliquely mounted on the optical path to upwardly reflect the fundus reflection light.
The imaging optical system 120 is further provided, for guiding the fundus reflection light reflected by the quick return mirror 127, with a field lens 128, a switching mirror 129, an eyepiece 130, a relay lens 131, a reflection mirror 132, an imaging lens 133 and an image pick up element 10a. The image pick up element 10a is an image pick up element such as CCD, etc. installed internally in the imaging device 10. On the touch panel monitor 11 a fundus oculi image Ef′ imaged by the image pick up element 10a is be displayed.
The switching mirror 129 is to be rotatable around the rotary shaft 129a as well as the quick return mirror 127. This switching mirror 129 is obliquely disposed on the optical path during observation with the naked eye and guides reflected light on the fundus oculi to the eyepiece 130.
Also, when a fundus image is formed by the imaging device 10, the switching mirror 129 is retracted from the optical path, and the fundus reflection light is guided toward an image pick-up element 10a. In this case, the fundus reflection light is directed toward a relay lens 131, is reflected by the mirror 132, and is focused on the image pick-up element 10a by the imaging lens 133.
Such a fundus camera 1000 is an ophthalmologic apparatus to be used for observing the state of the surface of a fundus oculi Ef, that is, the retina. In other words, a fundus camera 1000 is a ophthalmologic apparatus to obtain a 2-dimensional fundus oculi image when it sees the fundus oculi Ef from the corneal direction onto the eye E. On the other hand, in the deep layer of retina tissues such as the choroidea or sclera exist, technology for observing these deep layer tissues has been desired, but, in recent years, devices for observing these deep layer tissues have been practically implemented (e.g. JP Patent laid-open No. 2003-000543, JP Patent laid-open No. 2005-241464).
With the optical image measuring device disclosed in JP Patent laid-open No. 2003-000543 and JP Patent laid-open No. 2005-241464, low coherence light is split into two, one of which (signal light) is guided to a fundus oculi and the other one (reference light) is guided to a given reference object, and this is a device to form tomographic images of the surface and the deep layer tissue of a fundus oculi,and to form the 3-dimensional image from the tomographic images, by detecting and analyzing the interference light obtained by overlaying the signal light that has reached the fundus oculi and the reference light that has been reflected by the reference object. Such devices disclosed in JP Patent laid-open No. 2003-000543 are in general called a Fourier domain OCT.
The Fourier domain OCT is designed to form a tomographic image having a depth-wise cross-section along its scanning line by scanning and irradiating a signal light onto the fundus oculi. Such scanning of signal lights is referred to as a B-scan (see NEDO Workshop “Seeing (examining) inside the body from the ‘window’ of the human body, the fundus oculi”—Development of an ultra early diagnostic device for lifestyle-related diseases using the latest optical technologies (held on Apr. 25, 2005), Internet<URL: http://www.nedo.go.jp/informations/koubo/170627—2/besshi3.pdf>).
When forming a 3-dimensional image of fundus oculi of an eye, a B-scan is performed along a plurality of scanning lines, and an interpolation process is applied to the resulting plurality of tomographic images for the generation of 3-dimensional image data. This 3-dimensional image data is referred to as volume data, voxel data, and so forth, as well as medical imaging diagnosis devices such as an X-ray CT device, which is image data in a form in which pixel data (e.g. luminance value and RGB value regarding brightness, contrasting density and color) is assigned to each voxel. A 3-dimensional image is displayed as a pseudo 3-dimensional image seen from a certain viewing angle obtained by rendering volume data.
The axial length of an eye is employed in the positioning of IOL (Intraocular Lens) inserted into the eye, for example, in cataract surgery or the like, so it requires high measurement accuracy. In the measurement of axial length using ultrasonic waves, the accuracy of measurement is lower than methods using light since the wavelength of ultrasonic waves is relatively long (measurement error greater than the wavelength of the measurement waves occurs). Therefore, it is considered that distance in the oculus such as axial length should be determined using an optical method.
The present invention is based on the circumstances described above, with the purpose of providing an ophthalmologic apparatus allowing measurement of distance in the oculus using a new optical method.